1. Technical Field
This invention relates generally to pistons for internal combustion engines, and more particularly to pistons having a central oil cooling gallery.
2. Related Art
Piston constructions having a central oil cooling gallery or two substantially closed oil cooling galleries (dual galleries) are known. The dual gallery pistons have an annular, radially outer gallery and an open central gallery formed between upper and lower crown portions. The outer and central galleries can be isolated from one another or in fluid communication with one another via oil passages. In addition, it is known to provide pin lubrication passages extending from one or both of the galleries to a wrist pin. The lubrication passages can extend into a wrist pin bore of a pin boss and/or between laterally spaced pin bosses. The outer gallery is particularly suited for cooling a ring belt region of the piston, while the central gallery is particularly suited for cooling a central crown region formed in part by a combustion bowl wall, which is exposed to hot combustion gasses.
The combustion bowl and central crown region is exposed to extreme heat in use. As such, the aforementioned central galleries need to provide ample oil flow in order to provide adequately cooling to the central gallery region. Although central galleries, both closed and open, are known, issues remain in providing adequate cooling in the central crown region. In particular, continual efforts remain to both provide sufficient oil flow in the central crown region while at the same time avoiding “cooking” and deteriorating the oil. If the oil directed to the central gallery region is allowed to remain in the region for too long of a timeframe, the oil cooks, thereby diminishing both the cooling and lubrication functions of the oil. On the other hand, if the oil is allowed to flow outwardly from the central gallery too quickly, the cooling function of the oil is diminished in the central gallery region, thereby potentially reducing the useful life of the piston.